Burner for a gas turbine

ABSTRACT

A burner for a gas turbine, wherein the burner has a combustion chamber, a preheating device adapted to preheat air before it enters the combustion chamber and a swirler adapted to guide a swirler air flow that has the preheated air to the combustion chamber, wherein the swirler has a base plate with a surface that confines the swirler air flow, wherein the surface has a hole adapted to inject a liquid fuel into the swirler air flow and the base plate has a channel for transporting the liquid fuel to the hole, wherein at least a part of the channel is oriented essentially parallel to the surface so that the liquid fuel streams essentially parallel to the surface and is preheated by the swirler air flow.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2016/066333 filed Jul. 8, 2016, and claims the benefitthereof. The International Application claims the benefit of EuropeanApplication No. EP15176506 filed Jul. 13, 2015. All of the applicationsare incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a burner for a gas turbine.

BACKGROUND OF INVENTION

A burner for a gas turbine can be operated at certain operatingconditions by injecting water into the combustion chamber in order toreduce the flame temperature and therefore reducing the emission ofNO_(x). An alternative approach for reducing the emission of NO_(x) liesin using dry low emission (DLE) burners that are operated without theinjection of water and are based on premixing fuel and air prior tocombustion. DLE burners emit low concentrations of NO_(x) and producecompact flames. However, the DLE burners are conventionally designed fora full load operation. In particular, the DLE burners comprise fuellances for the injection of a liquid fuel into the combustion chamber,wherein the lances are sized such that an efficient atomisation of theliquid fuel and an efficient mixing of the fuel with air occurs at thefull load operation.

However, when the burner is operated at a part load operation, thepressure drop over the lances is lower in comparison to the full loadoperation, which results in a less efficient atomisation than at thefull load operation. This leads to a less efficient mixing of the fuelwith air and can lead to the formation of fuel ligaments that aredeposited on surfaces of the burner where it leads to the formation of acarbon build-up. When the carbon build-up is formed on the lances it canlead to an obstruction of the fuel and when this carbon build-up isformed at an igniter-port it can lead to a reduction in the efficiencyof ignition. Furthermore, the less efficient mixing of the fuel with aircan lead to the formation of soot that is emitted into the atmosphere.

Conventionally, at the part load operation the DLE combustor is operatedsuch that compressed air is bled from the gas turbine so that less airenters the combustion chamber which raises the flame temperature. Withthis higher temperature the carbon build-up can at least be partlyburned. However, this operation is disadvantageous since it reduces theefficiency of the gas turbine and can not be performed at a part load ofless than 40% of the full load.

SUMMARY OF INVENTION

It is therefore an object of the invention to provide a burner that canbe operated throughout the load range including a part load operationwith an efficient atomisation of a liquid fuel and an efficient mixingof the fuel with air.

The burner according to the invention for a gas turbine comprises acombustion chamber, a preheating device adapted to preheat air before itenters the combustion chamber and a swirler adapted to guide a swirlerair flow that comprises the preheated air to the combustion chamber,wherein the swirler comprises a wall with a surface that confines theswirler air flow, wherein the surface has a hole adapted to inject aliquid fuel into the swirler air flow and the wall has a channel fortransporting the liquid fuel to the hole, wherein at least a part of thechannel is oriented essentially parallel to the surface so that theliquid fuel can stream essentially parallel to the surface and can bepreheated by the swirler air flow. The viscosity of the liquid fuel isreduced when its temperature is increased by the preheating. This leadsadvantageously to an efficient atomisation of the liquid fuel andtherefore to an efficient mixing of the fuel with the air. Theatomisation and the mixing will also be efficient at a part loadoperation of the burner when the pressure drop of the liquid fuel overthe through hole is lower than at a full load operation of the burner.Furthermore, the hole requires a lower pressure drop for the atomisationof the liquid fuel in comparison to a fuel lance. Also for this reasonan efficient atomisation of the liquid fuel can take place at low partloads.

It is advantageous that the part of the channel which is orientedessentially parallel to the surface has a distance to the surface from 2mm to 10 mm. These values ensure an efficient heat transfer to theliquid fuel while maintaining the integrity of the wall. The diameter ofthe hole is advantageously from 0.5 mm to 3 mm. It is advantageous thatthe diameter of the channel in a plane perpendicular to the flowdirection of the liquid fuel is from 0.5 mm to 3 mm.

The material of the wall advantageously consists of carbon steel and/orsteel with 1 weight-% carbon. The carbon steel has a heat conductivityof 54 W/(m*K) and the steel with 1 weight-% carbon has a heatconductivity of 43 W/(m*K) which are much higher values than the heatconductivity of 16 W/(m*K) for the conventionally used stainless steel.

It is advantageous that the wall with the channel is formed byelectronic discharge machining, selective laser sintering and/orselective laser melting. With these techniques it is advantageouslypossible to form channels with complex geometries with many curves. Withthese complex geometries it is possible to bring a long section of thechannel close to the surface, hence making the heat transfer to theliquid fuel particularly efficient. The wall advantageously comprisestwo joint plates, wherein each plate comprises recesses that form a partof the channel. The recesses in the plates can be formed by milling thatis advantageously a simple and cost-efficient technique. It isadvantageous that the channel has the shape of a spiral. It isadvantageous that the channel has a meandering shape. With both shapesit is possible to bring a long section of the channel close to thesurface, hence making the heat transfer to the liquid fuel particularlyefficient.

It is advantageous that the burner comprises a compressor forcompressing the air before it enters the combustion chamber, whereby thetemperature of the air raises and the compressor forms the preheatingdevice. By preheating the air in this manner, it is advantageouslyachieved that the air is sufficiently hot for preheating the liquidfuel.

The burner comprises advantageously a further wall confining the swirlerair flow on the same side as and upstream with respect to the swirlerair flow from the wall and being displaced with respect to the wall in adirection towards the swirler air flow so that a step being able tocause a flow separation of the swirler air flow is formed by the walland the further wall. The flow separation caused by the step causes theformation of a vortex downstream with respect to the swirler air flow.Since the liquid fuel is injected via the through hole into the swirlerair flow and not by a lance that would protrude from the wall, theliquid fuel is directly mixed with the air when exiting the second walland therefore interacts with the vortex. Together with the low viscosityof the liquid fuel this interaction leads to a particular efficientatomisation of the liquid fuel and a particular efficient mixing withair.

It is advantageous that the combustion chamber is essentiallyrotationally symmetric around a burner axis and the step is located at aradial distance from the burner axis which is from r₁+0.2*(r₂−r₁) tor₁+0.8*(r₂−r₁), wherein r₁ is the radial distance from the burner axisto the radial inner end of the swirler and r₂ is the radial distancefrom the burner axis to the radial outer end of the swirler. The lowerboundary advantageously ensures an efficient interaction of the liquidfuel with the vortex. The upstream boundary advantageously ensures theformation of the vortex. The height of each step is advantageously from0.2*L to 0.5*L, wherein L is the distance from the step to the hole.This height advantageously ensures the formation of the vortex that isefficiently interacting with the liquid fuel. It is advantageous theheight of each step is maximum 15% of the swirler channel height,wherein the swirler channel height is the distance from the further wallto an opposite wall confining the swirler air flow and facing towardsthe wall. This maximum height advantageously avoids a large pressuredrop of the swirler air flow when passing the step.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned attributes and other features and advantages of thisinvention and the manner of attaining them will become more apparent andthe invention itself will be better understood by reference to thefollowing description of embodiments of the invention taken inconjunction with the accompanying drawings, wherein

FIG. 1 shows part of a gas turbine in a sectional view and in which thepresent inventive burner is incorporated,

FIG. 2 shows a longitudinal section of the burner and a part of thecombustor,

FIG. 3 shows a perspective view of a part of the a swirler of theburner,

FIG. 4 shows a sectional view of a part of the swirler with a firstchannel,

FIG. 5 shows a top view of the swirler,

FIG. 6 shows a perspective view of a part of the swirler with a secondchannel,

FIG. 7 shows a perspective view of a part of the swirler with a thirdchannel,

FIG. 8 shows a sectional view of a part of the swirler with a fourthchannel.

FIGS. 9 to 13 show different embodiments for holes of the swirler.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows an example of a gas turbine engine 10 in a sectional view.The gas turbine engine 10 comprises, in flow series, an inlet 12, acompressor section 14, a combustor section 16 and a turbine section 18which are generally arranged in flow series and generally about and inthe direction of a longitudinal or rotational axis 20. The gas turbineengine 10 further comprises a shaft 22 which is rotatable about therotational axis 20 and which extends longitudinally through the gasturbine engine 10. The shaft 22 drivingly connects the turbine section18 to the compressor section 14.

In operation of the gas turbine engine 10, air 24, which is taken inthrough the air inlet 12 is compressed by the compressor section 14 anddelivered to the combustion section or burner section 16. As part of thecompression process, the air temperature is normally raised from ambienttemperature to approximately 400-400° C., along with the raise in airpressure. The burner section 16 comprises a burner plenum 26, one ormore combustion chambers 28 and at least one burner 30 fixed to eachcombustion chamber 28. The combustion chambers 28 and the burners 30 arelocated inside the burner plenum 26. The compressed air preheatedthrough the compressor 14 enters a diffuser 32 and is discharged fromthe diffuser 32 into the burner plenum 26 from where a portion of theair enters the burner 30 and is mixed with a gaseous or liquid fuel. Theair/fuel mixture is then burned and the combustion gas 34 or working gasfrom the combustion is channelled through the combustion chamber 28 tothe turbine section 18 via a transition duct 17.

This exemplary gas turbine engine 10 has a cannular combustor sectionarrangement 16, which is constituted by an annular array of combustorcans 19 each having the burner 30 and the combustion chamber 28, thetransition duct 17 has a generally circular inlet that interfaces withthe combustor chamber 28 and an outlet in the form of an annularsegment. An annular array of transition duct outlets form an annulus forchannelling the combustion gases to the turbine 18.

The turbine section 18 comprises a number of blade carrying discs 36attached to the shaft 22. In the present example, two discs 36 eachcarry an annular array of turbine blades 38. However, the number ofblade carrying discs could be different, i.e. only one disc or more thantwo discs. In addition, guiding vanes 40, which are fixed to a stator 42of the gas turbine engine 10, are disposed between the stages of annulararrays of turbine blades 38. Between the exit of the combustion chamber28 and the leading turbine blades 38 inlet guiding vanes 44 are providedand turn the flow of working gas onto the turbine blades 38.

The combustion gas from the combustion chamber 28 enters the turbinesection 18 and drives the turbine blades 38 which in turn rotate theshaft 22. The guiding vanes 40, 44 serve to optimise the angle of thecombustion or working gas on the turbine blades 38.

The turbine section 18 drives the compressor section 14. The compressorsection 14 comprises an axial series of vane stages 46 and rotor bladestages 48. The rotor blade stages 48 comprise a rotor disc supporting anannular array of blades. The compressor section 14 also comprises acasing 50 that surrounds the rotor stages and supports the vane stages48. The guide vane stages include an annular array of radially extendingvanes that are mounted to the casing 50. The vanes are provided topresent gas flow at an optimal angle for the blades at a given engineoperational point. Some of the guide vane stages have variable vanes,where the angle of the vanes, about their own longitudinal axis, can beadjusted for angle according to air flow characteristics that can occurat different engine operations conditions.

The casing 50 defines a radially outer surface 52 of the passage 56 ofthe compressor 14. A radially inner surface 54 of the passage 56 is atleast partly defined by a rotor drum 53 of the rotor which is partlydefined by the annular array of blades 48.

The present invention is described with reference to the above exemplaryturbine engine having a single shaft or spool connecting a single,multi-stage compressor and a single, one or more stage turbine. However,it should be appreciated that the present invention is equallyapplicable to two or three shaft engines and which can be used forindustrial, aero or marine applications. It should be appreciated thatthe invention is equally applicable to burners used in e.g. annularcombustion chambers.

FIG. 2 shows that the burner 30 comprises an inner wall 101 thatconfines the combustion chamber 28 in a radial direction. Furthermore,the burner 30 comprises a pilot burner 104 and a main burner 105 thatare arranged on an axial end of the burner 30 and confine an axial endof the combustion chamber 28. The main burner 105 is arranged radiallyoutside from the pilot burner 104. The burner 30 comprises an outer wall102 that is arranged radially outside of the inner wall 101. The innerwall 101 and the outer wall 102 are essentially rotationally symmetricaround a burner axis 35 of the burner 30. In the operation of theburner, the air 24 is streamed in the space between the inner wall 101and the outer wall 102 towards the pilot burner 104 and the main burner105 as indicated by arrows 108, so that the inner wall 101 is cooled andthe air 24 is preheated before it enters the combustion chamber 28. Inthis manner the inner wall 101 and the outer wall 102 form a preheatingdevice for preheating the air.

The burner 30 comprises a swirler 107 located on the main burner 105 forswirling the air before it enters the combustion chamber 28. Afterpassing the space between the inner wall 101 and the outer wall 102 theair 24 passes through the swirler 107 in a direction towards the burneraxis 35 and enters the combustion chamber 28. The burner 30 isconfigured for dry operation only, i.e. it is not configured for theinjection of water into the combustion chamber 28.

The swirler 107 comprises a first axial end 113 that coincides with themain burner 105 and a second axial end 114 being located opposite to thefirst axial end 113. As it can be seen in FIGS. 3 and 5, the swirler 107furthermore comprises a multitude of swirler sectors or vanes 118 thatare in contact with the first axial end 113 and the second axial end114. The first axial end 113, the second axial end 114 and the swirlersectors 118 confine a swirler air flow 125. The swirler sectors 118 areshaped such that the air flow entering the combustion chamber 28 has aflow direction with respect to the burner axis 35, wherein the flowdirection essentially consists of a radial inward component and acomponent in circumferential direction. The swirler 107 comprises anannular array of vanes 118 (swirler sectors) extending from a base plateor wall 116 which define an annular array of passages for the swirlerairflow (125). The base plate 116 defines one of the surfaces of thepassages over which the swirler air flow 125 flows.

FIGS. 2 to 8 show that the swirler 107 comprises a wall or base plate116 with a surface that confines the swirler air flow 125 at the firstaxial end 113. The surface has a hole 103 adapted to inject a liquidfuel into the swirler air flow 125 and the wall has a channel 131 to 134for transporting the liquid fuel to the hole 103, wherein at least apart of the channel 131 to 134 is oriented essentially parallel to thesurface so that the liquid fuel can stream essentially parallel to thesurface and is partly preheated by the swirler air flow 125. The swirleritself incurs temperature input directly from the combustion flame andthe surrounding combustor or burner architecture. As it can be seen inFIGS. 3, 4 and 6 to 8, after leaving the hole 103 the liquid fuel isatomised and mixed with the swirler air flow 125 in an atomisationregion 119.

It is conceivable that the part of the channel 131 to 134 which isoriented essentially parallel to the surface has a distance to thesurface from 2 mm to 10 mm. It is furthermore conceivable that thediameter of the hole 103 is from 0.5 mm to 3 mm. It is conceivable thatthe diameter of the channel 131 to 134 in a plane perpendicular to theflow direction of the liquid fuel is from 0.5 mm to 3 mm. The wall 116consists of a material with high heat conductivity, for example carbonsteel and/or steel with 1 weight-% carbon. It is conceivable that thewall 116 with the channel 131 to 134 is formed by electronic dischargemachining, selective laser sintering and/or selective laser melting.

As it can be seen in FIGS. 3, 4, and 6 to 8 the burner 30 comprises afurther wall 115 confining the swirler air flow 125 on the same side asand upstream with respect to the swirler air flow 125 from the wall 116.The further wall 115 can be displaced with respect to the wall 116 in adirection towards the swirler air flow so that a step being able tocause a flow separation of the swirler air flow 125 is formed by thewall 116 and the further wall 115.

FIG. 4 shows the burner 30 with a first channel 131. The first channel131 has a meandering shape, wherein a multitude of sections of the firstchannel 131 are arranged next to each other in the axial direction withrespect to the burner axis 35. FIG. 6 shows the burner 30 with a secondchannel 132. The second channel 132 has a meandering shape, wherein thesection of the second channel 132 with the meandering shape is arrangedparallel to the surface of wall 116. FIG. 7 shows the burner 30 with athird channel 133. The third channel 133 has the shape of a spiral,wherein the hole 103 is located in the centre of the spiral. FIG. 8shows the burner 30 with a fourth channel 134. The fourth channel 134has a meandering shape, wherein a multitude of sections of the forthchannel 134 are arranged next to each other in the axial direction withrespect to the burner axis 35. The fourth channel 134 extends almostover the entire wall 116 for an effective heat transfer from the swirlerair flow 125 to the liquid fuel.

FIG. 4 shows the swirler 107 with the second channel 132 according toFIG. 6 and and the third channel 133 according to FIG. 7. As it can beseen in FIG. 4 a single hole 103 can be arranged between two neighbouredswirler sectors 108 or a multitude of holes can be arranged between twoneighboured swirler sectors 108.

FIGS. 9 to 13 show possible geometries for the holes 103. The first hole121 according to FIG. 9 has the shape of a circle with a missing sectorhaving an angle of 90°. The second hole 122 according to FIG. 10 has theshape of a ring. The hole 123 according to FIG. 11 consists of aplurality of elongate holes that are arranged tilted with respect toeach other. The hole 124 according to FIG. 12 has the form of a circle.FIG. 13 shows a perspective view of a plate 126 containing the hole 124according to FIG. 12. The holes 103 can be formed as an assembly ofseveral joint layers of metal.

Although the invention is described in detail by the preferredembodiment, the invention is not constrained by the disclosed examplesand other variations can be derived by the person skilled in the art,without leaving the extent of the protection of the invention.

1. A burner for a gas turbine, wherein the burner comprises: acombustion chamber, and a swirler, wherein the swirler comprises anannular array of vanes extending from a base plate which define anannular array of passages for guiding a swirler airflow, the base platedefines a surface of the passage over which the swirler air flow flows,wherein the surface has a hole adapted to inject a liquid fuel into theswirler air flow and the base plate has a channel for transporting theliquid fuel to the hole, wherein at least a part of the channel isoriented essentially parallel to the surface so that the liquid fuel isstreamed essentially parallel to the surface and is preheated.
 2. Theburner according to claim 1, wherein the part of the channel which isoriented essentially parallel to the surface has a distance to thesurface from 2 mm to 10 mm.
 3. The burner according to claim 1, whereinthe diameter of the hole is from 0.5 mm to 3 mm.
 4. The burner accordingto claim 1, wherein the diameter of the channel in a plane perpendicularto the flow direction of the liquid fuel is from 0.5 mm to 3 mm.
 5. Theburner according to claim 1, wherein the material of the base plateconsists of carbon steel and/or steel with 1 weight-% carbon.
 6. Theburner according to claim 1, wherein the base plate with the channel isformed by electronic discharge machining, selective laser sinteringand/or selective laser melting.
 7. The burner according to claim 1,wherein the base plate comprises two joint plates, wherein each platecomprises recesses that form a part of the channel.
 8. The burneraccording to claim 1, wherein the channel has the shape of a spiral. 9.The burner according to claim 1, wherein the channel has a meanderingshape.
 10. The burner according to claim 1, further comprising: acompressor for compressing the air before it enters the combustionchamber, whereby the temperature of the air raises and the compressorforms the preheating device.
 11. The burner according to claim 1,further comprising: a further wall confining the swirler air flow on thesame side as and upstream with respect to the swirler air flow from thebase plate and being displaced with respect to the base plate in adirection towards the swirler air flow so that a step being able tocause a flow separation of the swirler air flow is formed by the baseplate.
 12. The burner according to claim 1, wherein the combustionchamber is essentially rotationally symmetric around a burner axis andthe step is located at a radial distance from the burner axis which isfrom r₁+0.2*(r₂−r₁) to r₁+0.8*(r₂−r₁), wherein r₁ is the radial distancefrom the burner axis to the radial inner end of the swirler and r₂ isthe radial distance from the burner axis to the radial outer end of theswirler.
 13. The burner according to claim 1, wherein the height of eachstep is from 0.2*L to 0.5*L, wherein L is the distance from the step tothe hole.
 14. The burner according to claim 1, wherein the height ofeach step is maximum 15% of the swirler channel height (H), wherein theswirler channel height (H) is the distance from the further wall to anopposite wall confining the swirler air flow and facing towards the baseplate.
 15. The burner according to claim 1, further comprising: apreheating device adapted to preheat air before it enters the combustionchamber and the swirler adapted to guide the swirler air flow thatcomprises the preheated air to the combustion chamber.